Mostly park skating for me. So its snacks, water and skate tool. If the kids are with me its all about water and snacks to keep them energized and hydrated so they don't fade out and want to call it a day.

Board, backup deck in case of breakage, energy drink/water, cigarettes (smoke out/stretch before I leave), positive mental attitude. If I'm going to a gnarly/new spot I'll bring a broom and I have a block of wax in the car at all times.